The main raw material of Korean traditional paper (also referred to as “Hanji”) is the paper mulberry (Broussonetia kazinoki). Cellulose fibers extracted from the paper mulberry are relatively weak among bast fibers of the same kind and have short lengths. For these reasons, these fibers have been scarcely used for fiber products, have been limited to the production of papers and have been mainly used for the production of Korean traditional paper.
A method for producing Korean traditional paper is described hereafter.
Korean traditional paper has been produced by a paper-forming method comprising the following sequential processes: preparation of raw material; steaming, and drying in sunlight; beating; sheet formation; dewatering; drying; and finishing. Paper mulberry bark consists of a black outer bark and a white inner bark. To remove the black outer bark, that is, to facilitate the removal of the bark, the paper mulberry is first steamed. The boiled bark of the paper mulberry is peeled off to leave the white inner bark. The well-dried white bark is soaked in water for one or two days. The soaked bark is cut to a suitable size and boiled thoroughly in lye for 4-5 hours. Then, the boiled material is washed to remove the lye and dried in sunlight to bleach. Bumps of the washed and bleached material are removed by hand, and then the white bark is placed on a stone mortar and subjected to a beating process in which the paper mulberry fiber is pounded with a club for 40-60 minutes. In this process, the fiber disintegrates, and a thickener is added to the completely disintegrated fiber, which is then stirred well to achieve a uniform consistency.
Next, a sheet-forming process (called “Choji process” in Korean) is performed in which a net-shaped structure is immersed and moved backwards-and-forwards and side-to-side in a container containing the paper mulberry fiber. Although a process employing a single-net-shaped structure (“Oebal Choji”) traditionally used for sheet formation in making Korean traditional paper, an improved process employing a twin-net-shaped structure “Ssangbal Choji” has recently been frequently used. The net-shaped structures having a wet sheet laid thereon are stacked on each other with a pillow interposed between the wet sheets, and the wet sheets are pressed to remove water.
Finally, a finishing process is performed. In this process, dilute rice paste is applied to the surfaces of the incompletely dried sheets, which are then stacked in several tens of layers and pounded several hundred times with a wooden roller- or pestle-shaped article to make the sheets compact and smooth and increase the strength and gloss, thus obtaining finished Korean paper.
Recently, the Korean paper making process has been improved by introducing elements of Western paper making technology. A chemical substance such as sodium carbonate or sodium hydroxide is used instead of lye in the process of boiling the white bark. However, when the white bark is boiled with a strong alkaline chemical substance such as sodium hydroxide, a problem arises in that the fiber itself is damaged, resulting in loss of gloss of the resultant Korean paper, decreases in the strength and yield, and a great reduction in the quality. Further applications of Western paper technology include performing the beating process using a knife-type beater so as to increase productivity. Also, the disintegration (pulping) process is performed using a screw, and after the dissociation, a polymer such as polyacrylamide or polyethylene oxide is used as the thickener. In the drying process following the sheet forming process, the formed sheet is dried on an iron plate heated by steam. In addition, the finishing process is performed using a motor.
In the Korean paper making process, if the paper mulberry pulp in the wet state obtained by beating the white bark of the paper mulberry is dried as it is, the fiber becomes very hardened in an entangled state, thus making it substantially impossible to disintegrate the fiber. This is characteristic of bast fibers, wherein substances such as pectin and lignin bind the fibers and fibrous materials to each other in the drying process, thereby hardening the fibers. Such characteristics make the paper mulberry fiber suitable for papermaking, but act as the biggest obstacle to using the paper mulberry fiber in the production of other fiber products. Accordingly, currently, there is little or no product obtained using paper mulberry bast, other than as a raw material for making Korean traditional paper.